St. Louis County Police and Missouri State Highway Patrol troopers stand on guard as protesters march on West Florissant Avenue in Ferguson, Missouri on Aug. 9, 2015. Photo Credit: Getty Images / Michael B. Thomas

In an earlier column, I promised to take up the topic of the historical roots of the continuing mistrust between law enforcement and the black community. My intention in setting forth the background is not to impugn the integrity of police officers anywhere. Yet if we don't study the past we'll never understand the present, and the history of policing in America is deeply intertwined with the violence of racial oppression.

Those are not words I use lightly. Yet hard though it might be to believe, most historians nowadays accept that among the direct precursors to the modern police force were the slave-catching patrols of the old South.

In the late 18th and early 19th centuries, most Northern communities used a night-watch system, adopted from England, to keep order. The night watchman rarely made a circuit of the town, but stayed at his post, prepared to be summoned when a crime occurred. Where sheriffs existed, they were, in the 18th century, essentially tax collectors.

The slave patrols, by contrast, did what the name suggests -- they patrolled. Although their organization varied from place to place, in most of the South the members of the patrol were recruited from, and had special responsibility for, a particular small geographic area known as a "beat" - thus the origin of our contemporary term.

The slave patrols, the dreaded "paterollers," are remembered best for tracking down runaways and ferreting out potential uprisings, but many scholars think they had a more important day-to-day role. Those held in bondage in the South were seen as the greatest potential source of crime, including theft, assault, and sabotage of agricultural equipment. There was a steady traffic in pilferage, valuables being sold to free black railroad workers who would carry them North and resell them. By the reckoning of the slavocracy, the anti-crime patrols were being sent exactly where they were needed. Small surprise, then, that free white citizens were required to join the patrols if called.

Given recent events, it's a poignant historical irony that in the 1830s, the slave patrol of Charleston, South Carolina, had more members than any city police force in the North.

Despite legal codes purporting to control them, the patrollers were feared and reviled for their cruelty. A freedman named Lewis Garrard Clarke wrote that the patrols were "the tooth and tongue of serpents . the fool's cap of baboons ... the scum of stagnant pools ... the meanest, and lowest, and worst of all creation." And yet, for all their horrors, the slave patrols provided the template for the policing in its contemporary sense. Richmond, Virginia, created a full-time police force only after Gabriel Prosser led a slave uprising in 1800. Other cities followed suit. Yet three decades later, newspapers in Charleston complained that the police were too few to control the restive black population, and demanded an increase in the number of ... patrollers.

The North, meanwhile, continued to rely on variants of the watch system. As late as the early 19th century, law enforcement remained largely in the hands of citizens, who would band together to pursue miscreants. Unified police departments were not formed in Northern cities until the gang wars of the 1840s created the necessity. Immigrants saw the police as an institution created to keep them in their place - the same way black Southerners viewed the slave patrols.

Southerners considered their system superior to law enforcement in the North.

The Alabama lawyer Daniel R. Hundley, in his 1860 tract "Social Relations in Our Southern States," defended the patroller as being burdened with "a much more laborious duty to perform than his brother policeman of any Northern city."

In a spate of colorful vulgarity, Hundley attacked Northern critics "who are so grateful to the policeman who breaks the pate of the drunken Irish bully ... right under your parlor window; but go into hysterics at the bare mention of a Southern overseer's knocking down a refractory Hottentot."

Imbued with the police power of the state, the patrols worked under limitations that built upon the English common law and are familiar even today. They required a warrant to search slave quarters, for example, unless they had the permission of the owner. Patrollers who used too much force against runaways could be prosecuted. In the celebrated South Carolina case of State v. Boozer (1850), an entire patrol was fined after attacking a group of slaves gathered for a quilting, because the slaves all had "tickets" from their masters allowing them to attend. (The rules of course stemmed not from any solicitousness toward the enslaved, but from the felt need to protect the property of the masters.)

In the decades after the Civil War, the South continued to worry about its restive black population. One consequence was the replacement of the patrollers by the Ku Klux Klan, the Knights of the White Camelia, and other groups of night riders - - all described by their apologists as providing order in a lawless region. In the telling of the defeated South, the vicious Yankee occupiers refused to prosecute freedmen who broke the law, so private citizens had to take matters into their own hands.

Southerners, wrote the historian Walter Lynwood Fleming in 1905, saw the former slaves as "a sleeping volcano." Another consequence of Southern fear was an early version of community policing. Southern cities began hiring black officers in the decades after the Civil War in large part because they were thought to have expertise in how to deal with the formerly enslaved population, and because the existence of black police would keep the freedmen calm. (The black police, however, could not arrest whites.)

By that time, urban police forces in the North had come to serve as the hard edge of the political machines. The forces remained small relative to those in the South -- one reason that the anti-black and anti-Catholic riots during and after the Civil War so easily overwhelmed public authority. When at last the Northern police forces began to grow, they were organized very much on the model pioneered by the South. Officers walked beats and were expected to keep order largely through violence.

Brutality toward the black community was common.

Not until the Progressive Era did we see the true beginning of the professionalization of the police, with the establishment of formal training, academies and oversight. And not until after World War II was the goal truly attained. By that time, a certain image of police -- tough, well-armed, often cruel - was well-established in the popular imagination. The British police officer of the time still carried no weapon. The U.S., as so often, took a different path. Common to the penny dreadfuls of the early 20th century was the trope of the patrolman who is corrupt or abusive or both. And the image has never entirely faded.

As I said at the outset, my point certainly isn't to criticize police forces of today. But it's crucial for all of us, of every color, to recognize how each new incident of brutality constitutes a fresh and painful brushstroke on a canvas that the nation has been painting for centuries.